The thick plastic bag is likely HDPE (high density polyethylene) and is virtually impermeable.  Therefore there will be no gas exchange once the bag is sealed.
 

The garlic will respire even at low temperature and consume the oxygen in the sealed bag and produce carbon dioxide.  When there is no longer oxygen, there will be a shift to anaerobic respiration and carbon dioxide is produced without consuming oxygen, and therefore the bag will begin to inflate.   The shelf-life will be less in your condition than if more appropriate packaging were used since very high carbon dioxide concentrations (about 20%) will cause browning and eventual death of the cloves with time.  A simple solution is to have a small hole in the bag you currently use which allows some oxygen and some accumulation of carbon dioxide.  It will allow, though, escape of odor molecules as well.  The exact concentrations will depend on how large the hole is.  I do not have an example with garlic, but below is a table that illustrates this issue using retail bags of coleslaw held at 2 temperatures.  At the temperature abuse condition of 7.5°C, the bags have 0, 1 or 4 holes.   You probably need to select packaging that retains the garlic odor but has sufficient permeability so that anaerobic conditions are not developed. 

                                     —Marita Cantwell

Table 1. Example of the effect of holes in bags.  Effect of temperature and pinholes on gas composition of retail coleslaw.