Problem is similar to http://world.episerver.com/Forum/Developer-forum/EPiServer-7-CMS/Thread-Container/2013/2/Problems-with-Multiproperty/.
We just have a simple property (i.e. PageReference or string) after iisreset this property is null (in View Mode). In Edit Mode all values are fine, when I do changes in Edit Mode and save it - View Mode is fine as well.
It has something to do with caching. The workaround is to experiment with output cache... But it sometimes help and sometimes not... I don't understand what is happening.
Does anybody has similar issue?
Which patch version are you using?
We had a simular problem but it was with a custom property based on LongString where we didn't take in count the lazy loading part. That ment that if the first thing that happend after a reset was that a FindPagesWithCritera happend, null values was inserted into the cache, but it a getpage happend the right value went into the cache.
The solution for us was to inherit from ProprertyLongString instead of from PropertyData. Maby not what you are having, but might be something that can help in the search for the error.