Do weapon stats only apply when the weapon is active?

Solution 1:

Normally weapon stats only apply when the weapon is active, however there are a few exceptions to this, the pain train being just one example. The wearer gets both of the weapons benefits regardless of whether or not the weapon is active:

Weapons effects which take place without the weapon being active will be followed with "on wearer", like in the above example. These effects will also appear under the "Current on-wearer attributes" header on the character load out page:

Solution 2:

Damage increases/decreases are usually weapon-specific, meaning the buff/debuff only applies while that particular weapon is active. Other attributes, such as fire or explosive vulnerability, apply to the character as a whole no matter what the active weapon is.