Surrender Bug?

[Rossj]

Playing as France in 1796
Enland convinces Spain and Russia to declare war on France
Russia is preoccupied with Austria and Prussia and never make it to France
Eventually war with Russia expires
I send a force to Spain which meets inadquate resistance
I easilly capture Madrid and sit there for several turns
Spain's morale bottoms out, but they do not surrender
Then, I notice that a Spanish province turns red (England)
This seems odd, because I thought they were figting on Enland's behalf
I sit in Madrid for several more months, still no surrender
Then another province turns red
It appears that Spain is surrendering to England even though they are not at war and not to France who is sitting in their capital
It is quite annoying

[Rossj]

A follow-up
Oct 1800: I have already captured Madrid
Nov 1800: Portugal becomes an English protectorate
Feb 1801: Spanish morale bottoms out
Mar 1801: England acquires a Spanish province even though they are not at war with Spain at this time or in any of the preceding months
Aug 1801: I still controll Madrid, Spanish morale is zero, and England acquires yet another Spanish province