Yes, as there has been a number of online forums talking about growing molds found on an opened bucket of spackling paste.
You can also find loads of shared information on how to prevent molds from growing on your stored joint compound. This Youtube video shows you how to do it, and below is a sound advice from a contributor on Sawmillcreek.org:
If you want to keep mud around for a while, I've always found that cleaning the sides of the bucket off good, then totally flattening the top of the mud will in and of itself keep the mud from molding for quite a while. You do this each time you load up a mud pan (then snap the lid back on tightly). No chunks or mold. Oh, yeah, don't ever put mud from your pan back in the bucket--throw that out.
When buying spackling paste, you also have the option to choose on cured joint compounds that are rust/mildew resistant.
There are 4 critical requirements for mold growth – available mold spores, available mold food, appropriate temperatures and considerable moisture. The removal of any one of these items will prohibit mold growth.
Here are nine ways to curb moisture indoors and the mold that thrives on it, shared by Mother Nature Network.