[Veacari]

Currently on live, using your arbalest cannon skills disables some, but not all, passive effects gained from your offhand weapon.
Example: The hit bonus from a staff of eyes is lost when the weapon is no longer "equipped", and my understanding is that this is as intended.
The following bonuses, that rely on a specific offhand being equipped, persist despite the armament being "unequipped" by a cannon skill:

1) The attribute bonus from vent petale is not removed on the use of a cannon skill, the FP cost reduction is removed.
Tested by looking at the crit & hit values for attacks performed under the same conditions in debug mode

2) The attribute bonus from weapons is not removed on the use of a cannon skill
Tested with a mutated Nullifying Dirk for +5 Res, stats on double clicking character does not update, DR value on taking damage does not change: "reduc_multi was 76.048. (59.4695); 21.6 MAG DEF, ..." both before and after use of cannon skills.

The consequence is that this gives additional power to Howling Handshot on duelist / Arbalest setups, but also narrows the choice of offhand armaments.

[Autumn]

This appears to be correct, this was definitely a thing before 2.94 as I would commonly give up Vent Petale's bonus stats when I used Blowback Cannon. It may be related to the changes made to that skill.