According to Gustave Gautherot, a fawning biographer of Bourmont who had extensive access to his correspondence in the Bourmont family archives, Bourmont was trying to take leave from the army since June 1st. Clouet claims he talked him out of it, but that Bourmont was committed to leaving the army and crossing over to the enemy.
Stationed at Fontoy, Bourmont was less than 10 miles to the frontier. His 14th Division began its march to the Belgian frontier on June 8th.
It ended the 8th at Etain, having gone about 32 kilometers.
It ended the 9th at Sivry-sur-Meuse, having gone about 29 kilometers.
It ended the 10th at Mouzon, having gone about 32 kilometers.
So far, Bourmont appears to have been commanding diligently. However, suddenly things changed. On June 11th, the division only made 14 kilometers ending near Sedan. On the 12th it ended near Mouzon having only made 18 kilometers.
What could explain this sudden slow-down? Maybe the road quality changed, or maybe Bourmont had become aware that the march was to a concentration preceding military action. Napoleon historically kept his plans close to the vest, and thus this movement to the west was probably not explained.
As previously seen, Soult sent orders to Gérard urging an acceleration of his corps. And on cue, on June 13th Bourmont pushed his division 40 kilometers ending near Chimay.
This was quite an impressive march for someone we know would eventually desert his command and cross over to the enemy. Further, it had almost been two weeks since he reportedly had decided that he had to leave the army. His route was along the northern border, and he and his staff could have left at any time... but they didn't... something was keeping Bourmont at his post.
With the campaign delay, Napoleon decided to tweak the position of his army and push it closer to the frontier. The confidence to do this could be based on the fact that despite the intelligence the allies had gathered of French activity, and the frequent deserters, the Anglo-Dutch and Prussians forces had not yet made any significant movements to prepare for the French invasion. At most, Zieten's I Corps had been put on heightened alert.
Late in the evening of the 13th or in the early morning hours of the 14th, the Position of the Army on the 14th Order of the Day for June 14th was received. An excerpt for IV Corps reads:
The Armée de la Moselle will take a position in front of Philippeville tomorrow. Count Gérard will arrange to be able to leave on the day after tomorrow, the 15th, at 3 o’clock in the morning, to join the 3rd Corps and to press its movement on Charleroi, according to the new order that will be given to him; but General Gérard must especially guard his right flank and reconnoiter all the roads running to Charleroi and Namur.
Though it is often reported that at the time of Bourmont's defection, he lacked the Order of Movement of June 15, and thus could not provide any actionable intelligence to the Allies, we see here that at some point on June 14th, Bourmont, whose 14th Division was the Vanguard of the IV Corps, most likely became aware that he was to take positions near Philippeville and prepare for an attack on Charleroi.
Had Bourmont been privy to the entire order, he would learn that all three Columns Napoleon had assembled were to move on Charleroi. As Bourmont was very close to Gérard, this is highly likely.
Additionally, IV Corps, with Bourmont's 14th Division in the vanguard, was now going to take up positions near Philippeville - where Napoleon had originally intended III Corps to be.
As a result of Soult's "inexplicable" change to Napoleon's orders, the tip of the spear of the Right Column was now led by the only General known to have defected to the enemy, and who had suddenly responded to this opportunity by pushing his division harder and farther than he had at any previous point in the march.