There are 42 attributes with a SEQEND on layer "Dimensions" attached to the electrical blocks. By exploding the blocks, the seqend is removed and the attributes become text or attribute definitions, depending upon how you explode them.
The reason this happens is that when a block with attributes is inserted, SEQEND takes on the layer of the current layer. Subsequently changing the block and associated attributes to a different layer does not change the SEQEND entry.
To see this problem in action, create a completely new layer and set it current, insert a block with attributes on that layer, then change the layer of the block to a different layer, set a different layer current and try to purge the new layer. You will find it no longer will purge.
To correct this you can set the correct layer and re-insert the offending blocks or you can merge the offending layer with the electrical layer.