Why isn't Maple Valley, WA appreciating much anymore?

[Jack B.]

Last summer my rental in Maple Valley was worth about 450K based on comps. 

Then it went down to 425K. Even houses 5 doors down that were the EXACT same floor plan and age in the same subdivision were selling for 425K. It lost 25K in value over the year instead of going up. 

WTH?

I'm debating selling it and 1031 exchanging into more entry level properties in the 300-350K range.